Thyroid hormones

Question 1

Source

Answer 1

Follicles of thyroid

Most T3 formed in target tissue

Question 2

Function

Answer 2

1) Bone growth (synergistic with GH)
2) CNS maturation
3) increase B1 receptor in heart: raise CO, HR, SV, contractility

4) raise basal metabolic rate via increasing Na/K ATPase activity; increase O2 consumption, RR, body temp
5) increase glycolysis, gluconeogenesis, lipolysis

Question 3

Function of T3

Answer 3

1) brain maturation
2) bone growth
3) beta adrenergic effect
4) basal metabolic rate increases

Question 4

Tyroxine-binding globulin

Answer 4

Bind most T3/4 in blood, only free hormone is active

Decreased in hepatic failure,
Increased in pregnancy, or OCP use (estrogen increase it)

Question 5

T4

Answer 5

Major thyroid product;

converted to T3 in peripheral tissue by 5’-deiodinase

Question 6

T3

Answer 6

Binds receptor with greater affinity than T4

Question 7

Peroxidase

Answer 7

Responsible oxidation and organification of iodide as well as coupling of MIT and DIT

Question 8

Propylthiouracil and methimazole

Answer 8

Propylthiouracil: inhibit both peroxidase and 5’ deiodinase

Methimazole: inhibit peroxidase only

Question 9

Regulation

Answer 9

TRH (hypothal) stimulates TSH(ant pit), which stimulates follicular cells.

Negative feedback by free T3 to anterior pit to reduce sensitivity to TRH.

Thyroid stimulating immunoglobulin (TSI) like TSH, stimulates follicular cells in Graves disease

Question 10

Wolff-Chaikoff effect

Answer 10

Excess iodine temporarily inhibits thyroid peroxidase,

reduce iodine organification and decrease T3/T4 production.